Recommendation for amp

Assuming you will be at your desk while listening to the Harbeths, you wouldn't need a ton of power.  For a small footprint integrated amp, I would highly recommend the Rega Brio - it's half-size, 50wpc (8ohms), non-fatiguing sound.  

If you intend to sometimes listen from a distance and want to fill a larger space, then more power would be required.  

@smrex13 makes a great point, desktop application and small footprint desired... rega unit or psa sprout or w4s mint would work nicely - all with half wide chassis, decent sound

we all tend to spew out our favorites (myself guilty of this too) but it is important to note specifically what the op is asking for

+ on the Hegel. I audition the Rost and it was a really nice piece.

https://listenup.com/hegel-h90.html

This is a tidy package as well if you are ok with class D.  https://www.usaudiomart.com/details/649754296-ps-audio-stellar-strata-integrated-amplifier/

I would by a good class ab integrated used that would work out great for them you could get a great used amp for 2k that would light them up.